1. Technical Field
This disclosure generally relates to an image formation apparatus including a liquid discharging head, and especially relates to a liquid discharging head wherein a driving element is joined to a base member, and an image formation apparatus therewith.
2. Description of the Related Art
An ink jet recording apparatus is known as an exemplary image formation apparatus of a printer, a facsimile apparatus, a copying apparatus, a multi-function machine, and the like. A recording head of the ink jet recording apparatus uses a liquid discharging head, and recording (“image formation”, “imprinting”, and “printing”, are used as synonyms) is carried out on a recording medium such as recording paper. Although the recording medium may be called recording paper below, it is not limited to paper, but includes a recording medium, imprint paper, an imprint material, and a recording object. Recording is carried out by discharging an ink drop serving as recording liquid.
Examples of the liquid discharging head include an ink jet head, wherein pressure for pressurizing the liquid, i.e., the ink, contained in a liquid chamber is generated by a piezo-electric body. The piezo-electric body is often made of layers of internal electrodes and piezo-electric layers that are alternately arranged. Further, a wall surface of the liquid chamber is a diaphragm that is capable of elastic deformation, and is displaced in one of d33 and d31 directions by the piezo-electric body. The displacement causes a change in volume, and therefore, pressure in the liquid chamber; and an ink drop is discharged.
[Patent Reference 1] JPA 2003-211658
[Patent Reference 2] JPA 2004-322505
According to a conventional liquid discharging head as disclosed by Patent References 1, and 2, the width of a supporting substrate (base member) that is joined to a piezoelectric device is made less than the width of a piezoelectric vibrator.
Here, the conventional liquid discharging head as disclosed by Patent Reference 1 is described with reference to FIG. 16 and FIG. 17.
The conventional liquid discharging head includes
a passage plate 501 made of, e.g., a silicon substrate, forming two or more through-bores and independent liquid chambers serving as ink passages,
a nozzle plate 502 formed on the upper surface of the passage plate 501, having two or more discharging nozzles formed by, e.g., nickel electrocasting, and
a diaphragm 503 formed on the undersurface of the passage plate 501 formed by, e.g., nickel electrocasting. The three items above constitute the ink passage.
Further, an actuator unit is formed on the undersurface of the diaphragm 503, the actuator unit including a laminated type piezoelectric device 505 arranged in two columns on a base member 504 made of metal. On the outside of the piezoelectric device 505, a common ink passage 507 is formed by a frame member 506 that is joined to the diaphragm 503 such that the ink is supplied to each liquid chamber.
According to this liquid discharging head, a driving voltage is applied to the piezoelectric device 505, then a displacement occurs in the laminating direction of the piezoelectric device 505 (i.e., the vertical direction in the drawing), and the diaphragm 503 moves toward each of the liquid chambers, reducing the capacity of the liquid chambers, and causing the pressure inside the liquid chambers to rise. Accordingly, ink drops are discharged from the discharging holes (nozzles) of the nozzle plate 502 through a free passage.
As for the liquid discharging head using the driving element like the piezoelectric device, the driving element (piezoelectric device) that determines properties of the head accounts for a major portion of cost. In particular, the laminated type piezoelectric device is expensive; for this reason, the size of the piezoelectric device is desired to be as small as possible while maintaining the printing properties of the head.
The miniaturization of the driving element leads to miniaturization of the base member that is joined to the driving element. On the other hand, the height of the head cannot be made too small in consideration of arranging a roller for pressing down a recording medium at a portion near the head as much as possible when conveying the recording medium, and in consideration of obtaining capacity of a common liquid chamber 507 for supplying the recording liquid to the liquid chamber.
Consequently, the base member must have a high aspect ratio, i.e., small width and great height.
When, in general, using a laminated type piezoelectric device, after joining a piezoelectric device to a base member, the piezoelectric device is divided into individual driving elements (piezoelectric devices) by a slot process using a dicing saw or a wire saw.
In this case, when dividing the piezoelectric device into individual elements, the base member vibrates due to the stress generated in the piezoelectric device, and an individual piezoelectric device often falls over. The greater is the aspect ratio of the base member, the greater is the vibration caused by the stress. This remarkably degrades the yield when processing the piezoelectric device.
Specifically, with reference to FIG. 16 and FIG. 17, if the piezoelectric device 505 is miniaturized, the base member 504 is miniaturized, that is, its width D is decreased. On the other hand, the common liquid chamber 507 formed by the frame member 506 cannot be made too small because it has to provide sufficient liquid capacity, and in consideration of damping of the liquid vibration when printing. Since the height H of the actuator unit and the height H of the frame member 506 have to agree, the height H of the actuator unit cannot be decreased, which increases the aspect ratio of the base member 504. The great aspect ratio of the actuator unit causes the piezoelectric device 505 to vibrate due to the stress generated when dividing the piezoelectric device 505 into individual elements, which leads to falling over of an individual piezoelectric element, and exfoliation of an internal electrode.